Decode Ways--Leetcode

A message containing letters from was A-Z being encoded to numbers using the following mapping:

' A '-1 ' B '-2 ... ' Z '-26

given an encoded message containing digits, determine the total number of ways to decode it.

for example,
given encoded Message " , it could be decoded as " AB "   (1 2) Or " L "   ().

The number of ways decoding is "12" 2.

Basic ideas

Similar to the question climbing stairs

Before I, there are two ways to decode:

1. Section i-1 potential energy independent decode

2. I-2 and I-1, two together as a whole decode

Then the number of DEOCDE methods is the sum of the above two paths.

This code on the Leetcode, the implementation time is 5ms.

Class Solution {public:    int numdecodings (string s) {        if (S.empty ()) return 0;        int w2 = 1;        int w1 = s[0]! = ' 0 '? 1:0;        int w = W1;        for (int i=2; i<=s.size (); i++) {            w = (s[i-1] = = ' 0 ')? 0:w1;            if (s[i-2] = = ' 1 ' | | s[i-2] = = ' 2 ' && s[i-1] >= ' 0 ' && s[i-1] <= ' 6 ')                w + = W2;                        W2 = W1;            W1 = w;        }        Return w;    }};

Decode Ways--Leetcode